In automatic call-distribution (ACD) systems, calls incoming to a call center are answered and handled by a plurality of agents. The ACD system automatically distributes and connects incoming calls to whatever agents are suited to handle the calls and available, that is, not handling other calls at the moment.
It often happens that the call center becomes overloaded by calls, so that no suitable agents are available to handle calls at the moment that the calls come in. The calls then back up. They are placed in different queues based upon some preestablished criteria, and are placed in each queue in the order of their arrival and/or priority. There they await suitable agents becoming available to service them. The waiting calls are distributed to agents for handling on an oldest-call-waiting (OCW) basis. That is, when an agent becomes available, the system considers the call at the head of each queue from which that agent is eligible to handle a call, and selects the one of the calls that has been waiting the longest. The system does not take into consideration the unique service-time needs of different types of calls. For example, a video call may need to be serviced within tens of seconds of its arrival, and a voice-only call may need to be serviced within minutes, while e-mail may need a response within hours of its arrival.